Background Image/picture with margin spaces

I would like to add some image or maybe some color picture in the page background. However, I would like to leave some margin space.

The darker area is out of the page. The mais page color is white and the background is lightgray.

I use xelatex because of other resources.

See picture below:

You can use the background package, but indeed it can be tricky to get the position right! Please see the following example in which I set a random picture as background at fixed margins using the hshift and vshift settings, following your image:

% !TeX program  = xelatex
\documentclass{article}
\usepackage{background,lipsum}

\backgroundsetup{
scale=1,
color=black,
opacity=1,
contents={%
\includegraphics[%
height=\dimexpr\paperheight-2cm\relax, % double the vert. margin
width=\dimexpr\paperwidth-2cm\relax    % double the horiz. margin
]{example-image-a}
},
angle=0,
position = current page.south west,
nodeanchor = south west,
hshift = 1cm, % horizontal margin
vshift = 1cm  % vertical margin
}

\begin{document}
\lipsum[1-10]
\end{document}


I solved my question with this:

\usepackage{background}
\definecolor{myColor}{RGB}{234,234,234}
\backgroundsetup{
contents={
\begin{tikzpicture}
\fill[myColor] (0,0) rectangle (18.5,28);
\end{tikzpicture}
},
angle=0,
scale=1
}


Thanks for the help!